Prostate Specific Antigen Assay Standardization Bias Could Affect Clinical Decision Making

ArticleinThe Journal of urology 180(5):1959-62; discussion 1962-3 · October 2008with15 Reads
DOI: 10.1016/j.juro.2008.07.036 · Source: PubMed
Although prostate specific antigen is widely used to detect and manage prostate cancer, many patients and physicians are unaware of which prostate specific antigen assay is being used. Most commercial prostate specific antigen assays are standardized to the WHO 90:10 standard or aligned with the original Hybritech assay with potentially disparate results. A total of 1,916 men participated in a prostate cancer screening study in 2007. On the day of collection prostate specific antigen was tested from the same serum sample using the Access (Hybritech standard) and ADVIA Centaur (WHO 90:10 prostate specific antigen standard) assays. We examined the differences between the 2 assays and the effect that this might have on clinical decisions. Median prostate specific antigen was 0.9 and 1.05 ng/ml for the Centaur and Access assays, respectively, representing a 17% difference. Mean prostate specific antigen was 3.45 and 4.79 ng/ml, respectively, representing a 38% difference. Using a prostate specific antigen threshold of 2.5 ng/ml 5% of men would have been recommended to undergo biopsy using the Access but not the Centaur assay. Furthermore, prostate specific antigen differed by greater than 0.4 ng/ml in 26%, greater than 0.75 ng/ml in 14.5% and greater than 2 ng/ml in 4.5% of men in the same sample simply by using the different assays. In our prospective screening population median prostate specific antigen was 17% lower using WHO vs Hybritech based assay standardization. As such, if these assays were instead used on a serial basis in the same patient, this could lead to false acceleration or false deceleration in prostate specific antigen velocity. Thus, the assay may influence the likelihood of prostate biopsy and, thereby, prostate cancer detection.
    • "Drawbacks of PSA as a screening test include the diagnosis and treatment of some indolent tumors that would not have presented clinically and limitations in specificity whereby serum PSA levels may be elevated in benign prostatic conditions (benign prostatic hyperplasia, prostatitis) and urinary tract manipulation (eg, cystoscopy, prostate biopsy) [2]. In addition, recent studies have also shown variations in PSA levels according to genetic factors, obesity, certain medications, and standardization bias, adding to the complexity of its interpretation [3] [4] [5] [6] [7]. Despite these issues, there is general consensus that widespread PSA screening has led to a striking stage migration, with the vast majority of prostate cancers now diagnosed at a localized stage [8]. "
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